EP0274501B1 - Three point hitch velocity control - Google Patents
Three point hitch velocity control Download PDFInfo
- Publication number
- EP0274501B1 EP0274501B1 EP87904468A EP87904468A EP0274501B1 EP 0274501 B1 EP0274501 B1 EP 0274501B1 EP 87904468 A EP87904468 A EP 87904468A EP 87904468 A EP87904468 A EP 87904468A EP 0274501 B1 EP0274501 B1 EP 0274501B1
- Authority
- EP
- European Patent Office
- Prior art keywords
- signal
- magnitude
- hitch
- preselected
- control
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
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- G—PHYSICS
- G05—CONTROLLING; REGULATING
- G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
- G05D3/00—Control of position or direction
- G05D3/12—Control of position or direction using feedback
- G05D3/20—Control of position or direction using feedback using a digital comparing device
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- A—HUMAN NECESSITIES
- A01—AGRICULTURE; FORESTRY; ANIMAL HUSBANDRY; HUNTING; TRAPPING; FISHING
- A01B—SOIL WORKING IN AGRICULTURE OR FORESTRY; PARTS, DETAILS, OR ACCESSORIES OF AGRICULTURAL MACHINES OR IMPLEMENTS, IN GENERAL
- A01B63/00—Lifting or adjusting devices or arrangements for agricultural machines or implements
- A01B63/02—Lifting or adjusting devices or arrangements for agricultural machines or implements for implements mounted on tractors
- A01B63/10—Lifting or adjusting devices or arrangements for agricultural machines or implements for implements mounted on tractors operated by hydraulic or pneumatic means
- A01B63/111—Lifting or adjusting devices or arrangements for agricultural machines or implements for implements mounted on tractors operated by hydraulic or pneumatic means regulating working depth of implements
- A01B63/1117—Lifting or adjusting devices or arrangements for agricultural machines or implements for implements mounted on tractors operated by hydraulic or pneumatic means regulating working depth of implements using a hitch position sensor
Definitions
- This invention relates generally to an apparatus for controllably positioning a hitch of an agricultural vehicle, and more particularly, to an apparatus for positioning and controlling the instantaneous velocity of the hitch of an agricultural vehicle.
- the implements are usually interchangeably connected to the vehicle using a hitch arrangement which is typically powered via a hydraulic pump and cyclinder to controllably lift and lower the attached implement.
- a hitch arrangement which is typically powered via a hydraulic pump and cyclinder to controllably lift and lower the attached implement.
- These implements can typically vary from light duty cultivators to extremely large plows which have corresponding variations in mass.
- prior controls have typically employed an adjustable throttling device to limit hydraulic fluid flow to the hydraulic cylinders. For example, the hydraulic requirements to enable such a system to lift a heavy implement are excessive when compared to the hydraulic needs of a light implement.
- a system designed to lift the heaviest implement can cause undesirable velocities when employed on the lightest implement.
- a system with a single flow capacity for raising and lowering may give satisfactory operation when lowering a light implement, but when used on a heavy implement, the corresponding increase in hydraulic pressure can cause undesirably high rates of descent.
- the mass of the implement ultimately controls the velocity at which the hitch and implement descend and ascend.
- manufacturers of such systems have recognized these shortcomings and provided the adjustable throttling device which the operator may choose to manually adjust and limit flow based on his observation of the weight and configuration of the implement.
- US-A-4,529,089 attempts to overcome some of the problems set forth herein by conversion to an electronically controlled hitch positioner.
- it includes separate manually adjustable potentiometers for controlling the up and down rates of movement of the hitch; however, the rates are unaffected by the actual velocity or mass of the hitch. Rather, the potentiometers act only to control the duty cycle of an electrical signal delivered to a solenoid controlled hydraulic valve.
- This arrangement effectively provides a manually adjustable throttling device similar in operation to that of hydraulically controlled hitch positioners. It also suffers from coarse and unpredictable movement of the hitch as well as no provision for calibrating the solenoid-valve units.
- US-A-4571500 discloses an apparatus for selectively positioning a movable work element of a work vehicle at a plurality of preselected locations, the apparatus comprising a control element positionable at a plurality of preselected locations; a first sensing means for delivering a first signal having a magnitude correlative to the location of the control element; a second sensing means for delivering a second signal having a magnitude correlative to the location of the work element; comparator means for receiving the first and second signals and delivering a third signal having a magnitude correlative to the difference between the first and second signals; and means for receiving the second signal, differentiating the second signal, and delivering an actual velocity signal having a magnitude correlative to the velocity of the movable work element; and according to the invention, such an apparatus is characterised by means for receiving the third signal and delivering a desired velocity signal having a magnitude correlative to the magnitude of the third signal; means for receiving the actual and desired velocity signals and delivering a control signal having
- Fig. 1 illustrates a rubber belted agricultural vehicle 12 with a movable work element 14 pivotally connected to the rear frame portion 16 of the vehicle 12.
- the apparatus 10 selectively positions the movable work element 14 of the vehicle 12 at a plurality of preselected locations.
- the work element 14 is a three point hitch 17 and includes a pair of hydraulic cylinders 18, 20 extending between the hitch 17 and frame 16 to provide a hydraulic motive force to vertically raise and lower the hitch 17.
- the direction of fluid flow through the cylinders 18, 20 determines the direction of vertical motion and is controlled by a pair of solenoids 22, 24.
- solenoids 22, 24 are alternately actuated by a central electronic control 26 to selectively deliver pilot pressure to a hydraulic control system 28 and reverse the flow of hydraulic fluid through the cyclinders 18, 20 (a detailed description of the hydraulic control system 28 accompanies Fig. 2).
- a control element 30 is located within the operator's cab 32, and is manually positionable by the operator to a plurality of preselected locations.
- the element 30 consists of a hand operated friction type positional handle 34, wherein any position selected by the operator is frictionally maintained.
- a first sensing means 36 delivers a first signal having a magnitude correlative to the location of the control element 30.
- the first sensing means 36 can be any of a variety of position sensing electronic circuits, but preferably is a potentiometer with a tap connected to and movable with the handle 34.
- the output of the potentiometer is an analog signal with a variable voltage wherein the magnitude of the signal is directly proportional to the handle position.
- a pulse width modulating circuit converts the voltage level of the potentiometer to a variable duty cycle digital signal and delivers that signal to the central electronic control 26.
- a second sensing means 38 delivers a second signal having a magnitude correlative to the location of the work element 14.
- the second sensing means 38 is o the same variety as the first sensing means 36 and is preferably a potentiometer with a tap connected to and movable with the hitch 17.
- a variable duty cycle signal is similarly delivered by the second sensing means 38 to the central electronic control 26.
- Fig. 2 illustrates the hydraulic control system 28 and includes a variable displacement hydraulic pump 300 selectively connected to the hydraulic cylinder 18 through a pilot actuated three way valve 302. the solenoids 22, 24 are illustrated connected to opposite ends of the valve 302. The solenois 22, 24 are separately operable under electronic control to deliver a pilot pressure to the respective ends of the valve 302 and move the spool of the valve 22 to one of the actuated positions. For example, to initiate upward movement of the cylinder 18, the controller 26 energizes the up solenoid 22 which actuates the valve 302 and connects the cylinder 18 to the output of the pump 300.
- the controller 26 initiates downward movement of the cylinder 18 by energizing the down solenoid 24 which actuates the valve 302 and vents the cyclinder 18 to tank.
- the hydraulic control arrangement illustrated herein provides powered upward movement, but relies on gravity and the mass of the implement for downward movement.
- the hydraulic control system 28 includes a pressure feedback line 304 connected between the output of the three way valve 302 and the variable displacement hydraulic pump 300.
- the hydraulic control system 28 includes load sensing hydraulics of which the feedback line 304 forms an integral part.
- the pressure drop across the valve 302 acts to control the displacement of the hydraulic pump 300. As the pressure drop decreases, the pump displacement increases.
- the displacement of the pump 300 is sensitive to the valve stem opening and insensitive to the load.
- Figs 3a and 3b illustrate an electronic schematic of one embodiment of the present invention.
- Electrical connections 40, 42 are shown to be respectively interconnected with the first and second sensing means 36, 38.
- Pull up resistors 44, 46 are respectively connected between +8V and the electrical connections 40, 42.
- the "low" portions of the variable duty cycle signals delivered by the first and second sensing means 36, 38 pull the electrical connection points 40, 42 to system ground while the respective "high” portions allow the resistors 44, 46 to pull the connections points to a logically "high” level.
- a pair of low pass filters 48, 50 remove any spurious signals and pass dc signals which have a magnitude proportional to the duty cycles.
- Two inverters 52, 54 receive the signals and ensure that the output signal extends between ground and the positive rail.
- Noise induced in the wiring harness between the first and second sensing means 36, 38 and the electrical connections 40, 42 can level shift the variable duty cycle signal.
- the inverters 52, 54 output full range signals relative to the +5V digital circuitry power supply independent of any level shifting induced by the sensors or wiring harness.
- the outputs of the inverters 52, 54 are connected through a pair of low pass filters 53, 55 to a pair of inputs of a multiplexed analog to digital converter (A/D) 56.
- the output of the low pass filter 55 is also connected to a means 58 which receives the second signal indicative of the location of the hitch 17, differentiates the second signal, and delivers an actual velocity signal having a magnitude correlative to the velocity of the hitch 17.
- the means 58 includes a resistor 62 connected in series with a capacitor 64 between the inverter 54 output and the inverting input of an operational amplifier 66.
- the amplifier 66 functions as a differentiator by the connection of the capacitor 64 to the inverting input of the amplifier 66 and a feedback resistor 68 connected between the output and inverting input of the amplifier 66.
- a capacitor 70 connected in parallel with the feedback resistor 68 provides an upper frequency limit of differentiation while the resistor 62 provides the lower frequency limit of differentiation.
- the values of the resistor 62 and capacitor 70 are chosen with regard to closed loop stability and noise criteria.
- the noninverting input of the amplifier 66 is connected to a voltage divider network 72 to provide a fixed reference voltage.
- the divider network 72 includes a pair of resistors 74, 76 connected in series between +5V and ground.
- the midpoint of the resistors 74,76 is connected to the noninverting input of the amplifier 66 and to an input of the A/D 56.
- a capacitor 78 is connected in parallel with the resistor 76 to reduce electrical noise.
- the output of the amplifier 66 is also connected through a resistor 80 to an input of the AID 56 and to a voltage limiting circuit 82.
- the limiting circuit 82 includes a diode 84 and a resistor 86 connected in series between +5V and ground. The voltage drop across the resistor 86 is communicated to the bases of a pair of pnp type transistors 88, 90.
- the transistors 88, 90 each have a collector connected to ground and the emitter of the transistor 88 is connected to the output of the amplifier 66. Should the output of the amplifier exceed +5V, the transistor 88 will be biased “on” and connect the output of the amplifier to ground through the resistor 80.
- the voltage limiting circuit is intended to protect the AID 56 from excessive voltage.
- the emitter of the transistor 90 is connected to another input of the A/D 56 and to the output of an additional circuit.
- the operation of the transistor 90 is identical to that of the transistor 88 and serves to protect the A/D from excessive voltage from the additional circuit.
- An oscillator circuit 89 is connected to the clock input of the AID 56.
- the oscillator 89 is of conventional design and includes a Schmitt trigger 92 with an input connected to ground through a capacitor 94 and to its own output via a resistor 96.
- the oscillator 89 produces a clock signal for the AID 56 at a fixed frequency related to the values of the capacitor 94 and resistor 96.
- a microprocessor 98 is connected to the A/D 56 via a data port 100 for transferring the magnitude of the selected analog input signal from the A/D 56 as an 8-bit binary word.
- the analog signal is selected by the microprocessor 98 via an address port 102 which includes a start pulse 104 in the most significant bit of the address port 102.
- An end of conversion signal is delivered by the A/D 56 to the microprocessor on line 106 to signal when the 8-bit binary word on the data port 100 reflects the magnitude of the selected analog signal.
- the AID 56 used in the present embodiment is commercially available from National Semiconductor as part number ADC0809.
- the microprocessor operates under software control which can best be described by referring to the flowcharts shown in Figs. 4a, 4b, and 4c discussed later in this specification.
- An 8-bit output port 10 inteconnects the microprocessor 98 and a digital to analog converter (D/A) 10.
- the microprocessor 98 acts under software control to deliver an 8-bit binary word over the link 108 wherein the magnitude of the word is converted to an analog signal with a voltage of corresponding magnitude.
- the analog signal is delivered from the D/A 110 to the noninverting input of an operational amplifier 112 connected as a differential amplifier.
- An operational amplifier 118 is connected as a comparator and has an inverting input connected to the output of the amplifier 112 and a positive input connected to a triangle waveform generator 120.
- the triangle waveform generator 120 includes a pair of operational amplifiers 122, 124 each having a noninverting input connected to the voltage divider network 72.
- the amplifier 122 has an output connected through a resistor 126, inverter 128, and resistor 130 to its own inverting input.
- the amplifier 124 has an inverting input connected through a resistor 132 to the output of the inverter 128 and to its own output via a capacitor 134.
- the output of the amplifier 124 is connected to ground by a resistor 136, the noninverting input of the amplifier 118, and the inverting input of the amplifier 122 via a resistor 138.
- a logic circuit array 140 is connected to the output of amplifier 118 through a resistor 142 and acts to determine which of the up or down solenoids is selected.
- An output line 146 from the microprocessor 98 controls which of the solenoids is selected via software control.
- the line 146 is connected to both inputs of a NAND gate 148 acting as an inverter and to one input of a three input NOR gate 150.
- the output of the NAND gate 148 is connected to an input of a second three input NOR gate 152.
- Each of the NOR gates 150, 152 also receive an input from the amplifier 118 through the resistor 142.
- the output of the first NOR gate 150 is connected to the gate of an n-channel FET type transistor 154.
- the transistor 154 has a source connected to ground and a drain connected through a resistor 156 to the gate to a p-channel FET type power transistor 158.
- the transistor 158 has a source connected to battery voltage +B through a current sensing resistor 160 and a drain connected to the winding 162 of the down solenoid 164.
- the output of the second NOR gate 152 is connected to the gate of an n-channel FET type transistor 166.
- the transistor 166 has a source connected to ground and a drain connected through a resistor 168 to the gate of a p-channel FET type power transistor 170.
- the transistor 170 also has a source connected to battery voltage +B through the current sensing resistor 160 and a drain connected to the winding 172 of the up solenoid 174.
- Both of the power transistors 158, 170 each have a respective resistor 176, 178 and a light emitting diode (LED) 180, 182 connected to their drains whereby the LED 180, 182 is biased “on” when the transistor 158, 170 is biased “on”.
- the LEDs 180, 182 give a visual indication of the state of the solenoids 164, 174.
- Both of the windings 162, 172 are connected to ground through an n-channel FET type transistor 184 and a current sensing resistor 186.
- the transistor 184 forms an integral portion of an overcurrent protection circuit 188.
- the source of the transistor 184 is connected through a resistor 189 to the base of an npn type transistor 190.
- the transistor 190 has an emitter connected to ground and a collector connected to both inputs of a two inut NAND gate 192 so as to act as an invertr.
- a pull up resistor 194 normally connects the inputs of the NAND gate 192 to +5V and a capacitor 196 is used to limit noise.
- the output of the NAND gate 192 is connected to the gate of an n-channel FET type transistor 198 which has a source connected to ground and a drain connected to +8V through a pull up resistor 200 and to the gate of the transistor 184.
- the voltage drop across the current sensing resistor 186 biases the transistor 190 "on”.
- a "low” signal is delivered to the NAND gate 192 which biases the transistor 198 "on” and the transistor 184 "off” discontinuing the flow of current.
- the current sensing resistor 186 also provides a feedback signal indicative of the actual current flowing through the solenoids 164, 174. The actual current is then compared to the desired current by the operation amplifier 112.
- An operational amplifier 202 has a noninverting input connected through a resistor 204 to the current sensing resistor 186 and an inverting input connected to ground through a resistor 206 and to its own output via a resistor 208.
- the output of the amplifier 202 is a scaled version of the voltage drop across the current sensing resistor 186 and is delivered to the inverting input of the operational amplifier 112 through a resistor 210, an input port of the A/D 56, and the emitter of the transistor 90.
- the output of amplifier 112 is proportional to the difference between the actual and desired current levels and is compared to the triangle waveform by amplifier 118.
- the output of amplifier 118 is a fixed frequency variable duty cycle signal which ultimately controls the state of power transistors 158, 170 to influence the magnitude of the current flowing therein.
- the frequency of the signal has been selected to provide dither to the solenoid valves 164, 174 and help to prolong their lives by reducing crudding.
- a logic circuit 212 provides short circuit protection for both of the power transisitors 158, 170.
- the circuit 212 includes a pnp type transistor 214 which has an emitter connected to +B, a base connected through a resistor 216 to the sources of transistors 158, 170, and a collector connected to ground through a resistor 218 and one input of a NOR gate 220 via a resistor 222.
- the output of the NOR gate 220 is connected to both inputs of a two input NAND gate 224 acting as an inverter.
- the output of the NAND gate 224 is connected through a capacitor 226 to an input of the NOR gate 220 and to ground through a resistor 228 and a diode 230.
- the output of the NAND gate 224 is also connected to one input of both of the three input NOR gates 150, 152 and to an input port of the microprocessor 98.
- the voltage drop across the resistor 160 is sufficient to bias transistor 214 "on” and deliver a "high” signal to NOR gate 220.
- the NOR gate 220 outputs a "low' signal which is inverted by the NAND gate 224 causing both of the NOR gates 150, 152 to output "low” signals and bias transistors 158, 170 “off”.
- An additional operator input located in the cab 32 is connected to the central electronic control 26 and is normally "low", but can be switched to indicate that the operator would prefer to enter an alternate mode of operation. It is desirable to operate the control as an absolute open loop positioner when connecting an implement to the hitch 17.
- This alternate mode of operation is referred to as the hook-up mode and includes a mechanical single throw single pole switch (not shown) which has one pole connected to ground and another pole connected through an electrical connection and pull up resistor 231 to +8V.
- the second pole is also connected through a low pass filter 232 and an inverter 233 to the input of the microprocessor 98.
- a watchdog timer circuit 310 is provided to recognize if the microprocessor 98 should suffer from an intermittent error such that operation of the resident software routine is discontinued.
- the watchdog timer 310 not only recognizes the software error but also attempts to reset the microprocessor 98 and begin executing the software at the initial routines.
- the timer 310 includes a capacitor 312 and resistor 314 serially connected between an output of the microprocessor 98 and the base of an npn type transistor 316.
- An oscillator 318 includes a Schmitt trigger inverter 320 connected in parallel with a resistor 322 and a capacitor 324 connected between system ground and the input of the Schmitt trigger 320.
- the collector and emitter of the transistor 316 are connected across the capacitor 324 such that a "high" signal from the microprocessor 98 biases the transistor 316 "on” and shorts the capacitor potential to zero.
- the output of the oscillator 318 is connected to the reset input of the microprocessor 98.
- the software routine periodically shorts the capacitor to zero potential at a rate greater than the frequency of the oscillator 318, thereby preventing the output of the oscillator 318 from reaching a "high” level to reset the microprocessor 98. Should the software routine cease to execute properly, then the capacitor 324 will not be reset and the oscillator 318 will reset the microprocessor 98.
- the control signals the operator that an error is occurring by flashing a diagnostic LED 326.
- the output of the oscillator 318 is connected through a NAND gate 328 to the base of the npn type transistor 330.
- the transistor 330 has an emitter connected to system ground through a current limiting resistor 332 and a collector connected to battery voltage +B through the disagnostic LED 326.
- the oscillator 318 reaches a "high" level, not only is the microprocessor 98 reset, but the diagnostic LED 326 is also flashed at the frequency of the oscillator 318. If the microprocessor 98 fails to respond to the reset signal, the flashing LED signals the operator as to the type of failure.
- the control also has the ability to signal a number of different error messages to the operator via the diagnostic LED 326.
- Another output from the microprocessor 98 is connected to an input of the NAND gate 328 and to +5V via a pull up resistor 334.
- the software routine can energize the diagnostic LED 326 by placing a "low" signal on the output line.
- the type of error is communicated via a sequencing of the LED 326. For example, if a handle position is detected, which is outside the range of allowable movement, then the software flashes the LED 326 four times, pauses momentarily, and then repeats. Five flashes indicates that the hitch position signal is outside the acceptable range of movement. Similar codes can be established for a wide range of faults, thereby easing the job of troubleshooting a failed control.
- Figs. 4a, 4b and 4c a flowchart illustrates one embodiment of the software needed to operate the microprocessor 98.
- the software begins at block 234 by reaching the actual handle position and storing the instantaneous position in the variable P handle .
- the microprocessor outputs the address of the handle position input and a start pulse of the data link 102 and then monitors the end of conversion signal on line 106.
- the 8-bit word present on link 100 is read and stored as P handle .
- Control is transferred to block 235 where a desired hitch position is computed from the handle position and stored in the variable P des'
- the actual hitch position is read via an operation substantially similar to that of reading the actual handle position with the exception of the address presented on link 104 being that of the hitch position input.
- the actual hitch position is stored in variable Pact.
- the hitch position error is computed in block 238 by a means 239 which receives the actual and desired hitch position and delivers a signal correlative to the difference between the actual and desired hitch positions.
- the hitch position error is stored in the variable P err by using the formula:
- a means 241 receives the positional error signal and delivers a desired velocity signal which has a magnitude correlative to the magnitude of the positional error signal.
- the variable P err is multiplied by a constant k to convert the positional error into a desired velocity of the hitch 17.
- This simple equation ensures that as the positional error P err becomes greater, so too does the desired velocity V des . Unchecked, this proportional relationship could lead to a desired hitch velocity V des which is above recommended operating speeds.
- the relationship k(P. rr ) > V max is tested and if found to be true, then the desired velocity V des of the hitch 17 is set to a maximum allowable velocity V max in block 242. Conversely, if the tested relationship is false, then the desired velocity V des maintains its proportionality to the positional error and is set equal to k(P err ) in block 244.
- Control is transferred to block 246 where the actual hitch velocity is read by the microprocessor 98 via an operation similar to those performed in blocks 234, 236 and stored as the variable V act .
- a means 247 receives the actual and desired velocity signals and delivers a control signal which has a magnitude correlative to the difference between the actual and desired velocity signals.
- the magnitude of the corrective signal is determined in block 248 using the equation:
- a means receives the control signal and respectively controls the direction and velocity of movement of the hitch 17 in a direction to reduce the absolute magnitude of the positional error signal and the control signal.
- Block 250 forms the integral of the velocity error V err and transfers control to block 252.
- the sign of the positional error P err is used to determine the direction of desired movement and correspondingly, which of the solenoids 64, 74 is selected. If the positional error P err is greater than zero, the down solenoid is selected in block 254 by delivering a "low" signal from the microprocessor 98 on line 146 to enable NOR gate 150 to pass the variable duty cycle signal from the amplifier 118 to the transistor 158.
- the up solenoid is selected in block 256 by delivering a "high" signal from the microprocessor 98 on line 146 to enable NOR gate 152 to pass the variable duty cycle signal from the amplifier 118 to the transistor 170.
- a similar mode of operation occurs when the handle 34 is not moved for an extended period of time and yet the hitch 17 remains at a position higher than the desired position.
- the microprocessor 98 assumes that the hitch is unable to reach the commanded position due to either contact with the ground or a travel limiting stop. Should these conditions be satisfied, then control transfers to block 264 where the solenoid current is set to a minimal value to allow the hitch to float. Rather than fix the hitch position, it is desirable to allow the hitch to move up and down in contact with the ground surface.
- Movement of the hitch 17 is discontinued in response to the magnitude of the positional error signal P err being within a first preselected range.
- the software checks to determine if the hitch position is within an inner deadband. If the hitch has moved to within a preprogrammed distance of the desired position, then control transfers to the block 260 where the solenoid current is set to zero and movement of the hitch 17 ceases.
- the three way valve 302 returns to the center position and the pressure in the feedback line 304 falls off significantly, causing the variable position swashplate to move to a low pressure standby position. The load on the engine is subsequently reduced resulting in a higher fuel efficiency. If the positional error is outside the inner deadband, the solenoid current is unaffected for the moment and control transfers to a block 268 where the status of the hook up mode input is read.
- the handle position is closely monitored to determine if the operator truly desires to be in the hook up mode and actuation of the switch was not accidental.
- the operator To enter the hook up mode, the operator must position the handle 34 at the fully up, fully down, and middle position within a preselected duration of time. If the handle sequencing operation is not accomplished within the allotted time period, control transfers to the block 260 and the solenoid current is set to zero. Assuming that the sequencing operation is completed, a flag is set so that the operator need not reproduce the sequence while the switch remains actuated.
- the software reads the handle position in block 272 and respectively selects the up or down solenoid in blocks 274, 276 if the handle 34 is in the fully up position or fully down position. Subsequently, in block 278, the solenoid current is set to an intermediate constant value and causes a preselected rate of movement in the selected direction until the handle 34 is moved from the fully actuated position. A handle position other than fully up or fully down causes control to be transferred to the block 260 where solenoid current is set to zero. Operation in the hook up mode allows the operator to accurately and absolutely position the hitch 17 by placing the handle 34 at the fully actuated position until the hitch a17 reaches the desired position. When the hitch 17 reaches the desired position, the operator simply moves the handle 34 from the fully actuated position and causes the solenoid current to be set to zero.
- the status of a flag is checked to determine if the hitch position has been Inside the Inner deadband and Not Subsequently Outside an Outer deadband (IINSOO). If the flag is set, then control transfers to the block 260 and solenoid current is set to zero; however, if the flag is not set, then control transfers to block 282 where the solenoid current is set to the integral of the velocity error plus an offset t min .
- the IINSOO flag is necessary to allow the outer deadband to provide a hysteresis type effect during positioning of the hitch 17. Without the flag, the solenoid current would be set to zero when the positional error P err fell below the outer deadband. The hitch 17 would never reach the inner deadband. The outer deadband should only become operational subsequent to the hitch 17 reaching the inner deadband. Hence, the IINSOO flag is set when the positional error P err falls inside the inner deadband and is reset when the positional error Per, rises above the outer deadband.
- the solenoid offset current I min is the current necessary to induce movement of the hitch 17 at a minimum rate. Obviously, this current level is highly dependent upon a number of factors, including the individual solenoids and hydraulic components. It is therefore necessary to calibrate the offset current for each individual hitch control.
- a calibration mode can be entered in the software by executing a preselected sequence of handle 34 movements.
- the position of the hook-up mode switch is monitored so that movement of the switch between the "on” and "off” positions a total of three iterations causes software control to be transferred into a current sourcing mode.
- Actual handle position is read via the AID 56 in block 286.
- Decision block 288 compares the handle position to the upper limit of movement.
- the up solenoid is selected in block 290 and the solenoid current is set to the offset I min' Absent any movement of the handle 34 from the fully up position, the solenoid current will remain at the offset I min and the solenoid controlled valve can be manually adjusted until the hitch 17 begins to move upward.
- the handle position is compared to the lower limit in block 294.
- the handle 34 being at the fully lowered postiion transfers control to block 296 where the down solenoid is selected.
- the block 292 sets the solenoid current to the offset I min , and the solenoid controlled down valve can be manually adjusted until the hitch 17 begins to move downward.
- Software control can be returned to the main control routine by a power- down and power-up with the vehicle key switch.
- the solenoid current is set to a value which allows the hitch to "float". Rather than overheat the solenoid by continuing to deliver maximum current, the controller 26 reduces current to a "float" value and allows the hitch 17 and plow to move up and down with undulations in the ground surface. Alternately, the handle 34 can also request a position which is higher than the hitch 17 can reach. In this instance, it is not necessary that the hitch 17 be allowed to "float", but it is sufficient to simply maintain the hitch 17 at the maximum height it can reach. Accordingly, the current to the solenoid is reduced to zero and the hitch 17 remains at the fully raised position.
- the normal control mode can produce unexpected and undesirable movement of the hitch 17.
- the handle 34 is requesting a position which the hitch 17 has reached, but due to a slight leakage of hydraulic fluid, the hitch 17 slowly descends until it reaches the outer deadband limit.
- the controller 26 will energize the up solenoid and move the hitch 17 toward the desired position.
- This unexpected movement can cause misalignment of the hitch and plow and resultant difficulties in their connection.
- the operator enters an alternate mode of operation by actuating a switch and operating the handle through a preselected sequence of movements.
- the operator causes the hitch 17 to move up or down at a preselected rate by moving the handle 34 to the respective up and down limits of travel.
- the operator can now jog the hitch 17 into the desired position by selective movement of the handle 34 between an extreme position and a midrange position.
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Abstract
Description
- This invention relates generally to an apparatus for controllably positioning a hitch of an agricultural vehicle, and more particularly, to an apparatus for positioning and controlling the instantaneous velocity of the hitch of an agricultural vehicle.
- In the field of agricultural vehicles, it is commonplace for a single vehicle to be used in a wide variety of applications and to tow a broad spectrum of implements. The implements are usually interchangeably connected to the vehicle using a hitch arrangement which is typically powered via a hydraulic pump and cyclinder to controllably lift and lower the attached implement. These implements can typically vary from light duty cultivators to extremely large plows which have corresponding variations in mass. To maintain the controllability of the hitch, prior controls have typically employed an adjustable throttling device to limit hydraulic fluid flow to the hydraulic cylinders. For example, the hydraulic requirements to enable such a system to lift a heavy implement are excessive when compared to the hydraulic needs of a light implement. A system designed to lift the heaviest implement can cause undesirable velocities when employed on the lightest implement. Conversely, a system with a single flow capacity for raising and lowering may give satisfactory operation when lowering a light implement, but when used on a heavy implement, the corresponding increase in hydraulic pressure can cause undesirably high rates of descent. The mass of the implement ultimately controls the velocity at which the hitch and implement descend and ascend. Heretofore, manufacturers of such systems have recognized these shortcomings and provided the adjustable throttling device which the operator may choose to manually adjust and limit flow based on his observation of the weight and configuration of the implement.
- Unfortunately, such manually adjustable systems have some obvious shortcomings. Selection of a fluid flow rate to limit the descent of an implement to an acceptable rate also acts to limit the ascent of the implement in direct opposition to the desired effect. As the mass of the implement increases, so too does the speed with which it descends, however, the inverse is also true. As the mass of the implement increases, the speed with which it ascends decreases. Therefore, any action to limit the flow to decrease the rate of descent further decreases the rate of ascent, resulting in limited performance during raising of the implement. Further, a manual system is only effective when properly adjusted and cannot compensate for an operator's forgetfullness or inattention.
- US-A-4,529,089 attempts to overcome some of the problems set forth herein by conversion to an electronically controlled hitch positioner. In particular, it includes separate manually adjustable potentiometers for controlling the up and down rates of movement of the hitch; however, the rates are unaffected by the actual velocity or mass of the hitch. Rather, the potentiometers act only to control the duty cycle of an electrical signal delivered to a solenoid controlled hydraulic valve. This arrangement effectively provides a manually adjustable throttling device similar in operation to that of hydraulically controlled hitch positioners. It also suffers from coarse and unpredictable movement of the hitch as well as no provision for calibrating the solenoid-valve units.
- US-A-4571500 discloses an apparatus for selectively positioning a movable work element of a work vehicle at a plurality of preselected locations, the apparatus comprising a control element positionable at a plurality of preselected locations; a first sensing means for delivering a first signal having a magnitude correlative to the location of the control element; a second sensing means for delivering a second signal having a magnitude correlative to the location of the work element; comparator means for receiving the first and second signals and delivering a third signal having a magnitude correlative to the difference between the first and second signals; and means for receiving the second signal, differentiating the second signal, and delivering an actual velocity signal having a magnitude correlative to the velocity of the movable work element; and according to the invention, such an apparatus is characterised by means for receiving the third signal and delivering a desired velocity signal having a magnitude correlative to the magnitude of the third signal; means for receiving the actual and desired velocity signals and delivering a control signal having a magnitude correlative to the absolute difference between the actual and desired velocity signals; and means for receiving the control signal and respectively controlling the direction and velocity of movement of the work element in a direction to reduce the absolute magnitude of the third signal and the control signal.
- In the accompanying drawings:
- Fig. 1 illustrates a diagrammatic view of the vehicle, hitch system, and a block diagram of an embodiment of the present invention;
- Fig. 2 illustrates an hydraulic schematic of an embodiment of the hydraulic circuitry of the present invention;
- Fig. 3 illustrates an electrical schematic of an embodiment of the electronic circuitry of the present invention;
- Fig. 4a illustrates a flowchart of an embodiment of the present invention;
- Fig. 4b illustrates a flowchart of an embodiment of the present invention; and
- Fig. 4c illustrates a flowchart of an embodiment of the present invention.
- Referring now to the drawings, wherein a preferred embodiment of the
present apparatus 10 is shown, Fig. 1 illustrates a rubber beltedagricultural vehicle 12 with amovable work element 14 pivotally connected to the rear frame portion 16 of thevehicle 12. Theapparatus 10 selectively positions themovable work element 14 of thevehicle 12 at a plurality of preselected locations. In the preferred embodiment, thework element 14 is a threepoint hitch 17 and includes a pair ofhydraulic cylinders 18, 20 extending between thehitch 17 and frame 16 to provide a hydraulic motive force to vertically raise and lower thehitch 17. The direction of fluid flow through thecylinders 18, 20 determines the direction of vertical motion and is controlled by a pair ofsolenoids solenoids electronic control 26 to selectively deliver pilot pressure to ahydraulic control system 28 and reverse the flow of hydraulic fluid through thecyclinders 18, 20 (a detailed description of thehydraulic control system 28 accompanies Fig. 2). - A control element 30 is located within the operator's
cab 32, and is manually positionable by the operator to a plurality of preselected locations. Preferably, the element 30 consists of a hand operated friction type positional handle 34, wherein any position selected by the operator is frictionally maintained. A first sensing means 36 delivers a first signal having a magnitude correlative to the location of the control element 30. The first sensing means 36 can be any of a variety of position sensing electronic circuits, but preferably is a potentiometer with a tap connected to and movable with the handle 34. The output of the potentiometer is an analog signal with a variable voltage wherein the magnitude of the signal is directly proportional to the handle position. A pulse width modulating circuit converts the voltage level of the potentiometer to a variable duty cycle digital signal and delivers that signal to the centralelectronic control 26. - A second sensing means 38 delivers a second signal having a magnitude correlative to the location of the
work element 14. The second sensing means 38 is o the same variety as the first sensing means 36 and is preferably a potentiometer with a tap connected to and movable with thehitch 17. A variable duty cycle signal is similarly delivered by the second sensing means 38 to the centralelectronic control 26. - Fig. 2 illustrates the
hydraulic control system 28 and includes a variable displacementhydraulic pump 300 selectively connected to thehydraulic cylinder 18 through a pilot actuated threeway valve 302. thesolenoids valve 302. Thesolenois valve 302 and move the spool of thevalve 22 to one of the actuated positions. For example, to initiate upward movement of thecylinder 18, thecontroller 26 energizes the upsolenoid 22 which actuates thevalve 302 and connects thecylinder 18 to the output of thepump 300. Similarly, thecontroller 26 initiates downward movement of thecylinder 18 by energizing the downsolenoid 24 which actuates thevalve 302 and vents thecyclinder 18 to tank. The hydraulic control arrangement illustrated herein provides powered upward movement, but relies on gravity and the mass of the implement for downward movement. Further, thehydraulic control system 28 includes apressure feedback line 304 connected between the output of the threeway valve 302 and the variable displacementhydraulic pump 300. Thehydraulic control system 28 includes load sensing hydraulics of which thefeedback line 304 forms an integral part. The pressure drop across thevalve 302 acts to control the displacement of thehydraulic pump 300. As the pressure drop decreases, the pump displacement increases. The displacement of thepump 300 is sensitive to the valve stem opening and insensitive to the load. - Figs 3a and 3b illustrate an electronic schematic of one embodiment of the present invention.
Electrical connections 40, 42 are shown to be respectively interconnected with the first and second sensing means 36, 38. Pull upresistors electrical connections 40, 42. Thus, the "low" portions of the variable duty cycle signals delivered by the first and second sensing means 36, 38 pull theelectrical connection points 40, 42 to system ground while the respective "high" portions allow theresistors low pass filters 48, 50 remove any spurious signals and pass dc signals which have a magnitude proportional to the duty cycles. Twoinverters electrical connections 40, 42 can level shift the variable duty cycle signal. Theinverters - The outputs of the
inverters low pass filter 55 is also connected to ameans 58 which receives the second signal indicative of the location of thehitch 17, differentiates the second signal, and delivers an actual velocity signal having a magnitude correlative to the velocity of thehitch 17. The means 58 includes aresistor 62 connected in series with acapacitor 64 between theinverter 54 output and the inverting input of anoperational amplifier 66. Theamplifier 66 functions as a differentiator by the connection of thecapacitor 64 to the inverting input of theamplifier 66 and afeedback resistor 68 connected between the output and inverting input of theamplifier 66. A capacitor 70 connected in parallel with thefeedback resistor 68 provides an upper frequency limit of differentiation while theresistor 62 provides the lower frequency limit of differentiation. The values of theresistor 62 and capacitor 70 are chosen with regard to closed loop stability and noise criteria. The noninverting input of theamplifier 66 is connected to avoltage divider network 72 to provide a fixed reference voltage. Thedivider network 72 includes a pair ofresistors 74, 76 connected in series between +5V and ground. The midpoint of theresistors 74,76 is connected to the noninverting input of theamplifier 66 and to an input of the A/D 56. Acapacitor 78 is connected in parallel with the resistor 76 to reduce electrical noise. The output of theamplifier 66 is also connected through aresistor 80 to an input of theAID 56 and to avoltage limiting circuit 82. - The limiting
circuit 82 includes adiode 84 and aresistor 86 connected in series between +5V and ground. The voltage drop across theresistor 86 is communicated to the bases of a pair ofpnp type transistors 88, 90. Thetransistors 88, 90 each have a collector connected to ground and the emitter of the transistor 88 is connected to the output of theamplifier 66. Should the output of the amplifier exceed +5V, the transistor 88 will be biased "on" and connect the output of the amplifier to ground through theresistor 80. The voltage limiting circuit is intended to protect theAID 56 from excessive voltage. Similarly, the emitter of thetransistor 90 is connected to another input of the A/D 56 and to the output of an additional circuit. The operation of thetransistor 90 is identical to that of the transistor 88 and serves to protect the A/D from excessive voltage from the additional circuit. Anoscillator circuit 89 is connected to the clock input of theAID 56. Theoscillator 89 is of conventional design and includes a Schmitt trigger 92 with an input connected to ground through acapacitor 94 and to its own output via aresistor 96. Theoscillator 89 produces a clock signal for theAID 56 at a fixed frequency related to the values of thecapacitor 94 andresistor 96. - A
microprocessor 98 is connected to the A/D 56 via adata port 100 for transferring the magnitude of the selected analog input signal from the A/D 56 as an 8-bit binary word. The analog signal is selected by themicroprocessor 98 via anaddress port 102 which includes astart pulse 104 in the most significant bit of theaddress port 102. An end of conversion signal is delivered by the A/D 56 to the microprocessor online 106 to signal when the 8-bit binary word on thedata port 100 reflects the magnitude of the selected analog signal. TheAID 56 used in the present embodiment is commercially available from National Semiconductor as part number ADC0809. The microprocessor operates under software control which can best be described by referring to the flowcharts shown in Figs. 4a, 4b, and 4c discussed later in this specification. - An 8-
bit output port 10 inteconnects themicroprocessor 98 and a digital to analog converter (D/A) 10. Themicroprocessor 98 acts under software control to deliver an 8-bit binary word over thelink 108 wherein the magnitude of the word is converted to an analog signal with a voltage of corresponding magnitude. The analog signal is delivered from the D/A 110 to the noninverting input of anoperational amplifier 112 connected as a differential amplifier. A parallel combination of aresistor 114 andcapacitor 116 are connected between the output and inverting input of theamplifier 112. Anoperational amplifier 118 is connected as a comparator and has an inverting input connected to the output of theamplifier 112 and a positive input connected to atriangle waveform generator 120. - The
triangle waveform generator 120 includes a pair ofoperational amplifiers voltage divider network 72. Theamplifier 122 has an output connected through a resistor 126, inverter 128, andresistor 130 to its own inverting input. Theamplifier 124 has an inverting input connected through a resistor 132 to the output of the inverter 128 and to its own output via a capacitor 134. The output of theamplifier 124 is connected to ground by aresistor 136, the noninverting input of theamplifier 118, and the inverting input of theamplifier 122 via aresistor 138. - A logic circuit array 140 is connected to the output of
amplifier 118 through aresistor 142 and acts to determine which of the up or down solenoids is selected. Anoutput line 146 from themicroprocessor 98 controls which of the solenoids is selected via software control. Theline 146 is connected to both inputs of aNAND gate 148 acting as an inverter and to one input of a three input NORgate 150. The output of theNAND gate 148 is connected to an input of a second three input NORgate 152. Each of the NORgates amplifier 118 through theresistor 142. - The output of the first NOR
gate 150 is connected to the gate of an n-channel FET type transistor 154. The transistor 154 has a source connected to ground and a drain connected through aresistor 156 to the gate to a p-channel FETtype power transistor 158. Thetransistor 158 has a source connected to battery voltage +B through acurrent sensing resistor 160 and a drain connected to the winding 162 of thedown solenoid 164. Similarly, the output of the second NORgate 152 is connected to the gate of an n-channelFET type transistor 166. Thetransistor 166 has a source connected to ground and a drain connected through aresistor 168 to the gate of a p-channel FETtype power transistor 170. Thetransistor 170 also has a source connected to battery voltage +B through thecurrent sensing resistor 160 and a drain connected to the winding 172 of theup solenoid 174. Both of thepower transistors respective resistor LED 180, 182 is biased "on" when thetransistor LEDs 180, 182 give a visual indication of the state of thesolenoids - Both of the
windings FET type transistor 184 and acurrent sensing resistor 186. Thetransistor 184 forms an integral portion of anovercurrent protection circuit 188. The source of thetransistor 184 is connected through a resistor 189 to the base of annpn type transistor 190. Thetransistor 190 has an emitter connected to ground and a collector connected to both inputs of a twoinut NAND gate 192 so as to act as an invertr. A pull upresistor 194 normally connects the inputs of theNAND gate 192 to +5V and acapacitor 196 is used to limit noise. The output of theNAND gate 192 is connected to the gate of an n-channelFET type transistor 198 which has a source connected to ground and a drain connected to +8V through a pull upresistor 200 and to the gate of thetransistor 184. When the current exceeds a preselected limit, the voltage drop across thecurrent sensing resistor 186 biases thetransistor 190 "on". A "low" signal is delivered to theNAND gate 192 which biases thetransistor 198 "on" and thetransistor 184 "off" discontinuing the flow of current. - The
current sensing resistor 186 also provides a feedback signal indicative of the actual current flowing through thesolenoids operation amplifier 112. Anoperational amplifier 202 has a noninverting input connected through aresistor 204 to thecurrent sensing resistor 186 and an inverting input connected to ground through a resistor 206 and to its own output via a resistor 208. The output of theamplifier 202 is a scaled version of the voltage drop across thecurrent sensing resistor 186 and is delivered to the inverting input of theoperational amplifier 112 through aresistor 210, an input port of the A/D 56, and the emitter of thetransistor 90. The output ofamplifier 112 is proportional to the difference between the actual and desired current levels and is compared to the triangle waveform byamplifier 118. The output ofamplifier 118 is a fixed frequency variable duty cycle signal which ultimately controls the state ofpower transistors solenoid valves - A
logic circuit 212 provides short circuit protection for both of thepower transisitors circuit 212 includes apnp type transistor 214 which has an emitter connected to +B, a base connected through aresistor 216 to the sources oftransistors resistor 222. The output of the NOR gate 220 is connected to both inputs of a twoinput NAND gate 224 acting as an inverter. The output of theNAND gate 224 is connected through a capacitor 226 to an input of the NOR gate 220 and to ground through aresistor 228 and a diode 230. The output of theNAND gate 224 is also connected to one input of both of the three input NORgates microprocessor 98. During a short circuit condition, the voltage drop across theresistor 160 is sufficient tobias transistor 214 "on" and deliver a "high" signal to NOR gate 220. The NOR gate 220 outputs a "low' signal which is inverted by theNAND gate 224 causing both of the NORgates bias transistors - An additional operator input located in the
cab 32 is connected to the centralelectronic control 26 and is normally "low", but can be switched to indicate that the operator would prefer to enter an alternate mode of operation. It is desirable to operate the control as an absolute open loop positioner when connecting an implement to thehitch 17. This alternate mode of operation is referred to as the hook-up mode and includes a mechanical single throw single pole switch (not shown) which has one pole connected to ground and another pole connected through an electrical connection and pull upresistor 231 to +8V. The second pole is also connected through alow pass filter 232 and aninverter 233 to the input of themicroprocessor 98. - A
watchdog timer circuit 310 is provided to recognize if themicroprocessor 98 should suffer from an intermittent error such that operation of the resident software routine is discontinued. Thewatchdog timer 310 not only recognizes the software error but also attempts to reset themicroprocessor 98 and begin executing the software at the initial routines. Thetimer 310 includes acapacitor 312 andresistor 314 serially connected between an output of themicroprocessor 98 and the base of annpn type transistor 316. Anoscillator 318 includes aSchmitt trigger inverter 320 connected in parallel with aresistor 322 and acapacitor 324 connected between system ground and the input of theSchmitt trigger 320. The collector and emitter of thetransistor 316 are connected across thecapacitor 324 such that a "high" signal from themicroprocessor 98 biases thetransistor 316 "on" and shorts the capacitor potential to zero. The output of theoscillator 318 is connected to the reset input of themicroprocessor 98. The software routine periodically shorts the capacitor to zero potential at a rate greater than the frequency of theoscillator 318, thereby preventing the output of theoscillator 318 from reaching a "high" level to reset themicroprocessor 98. Should the software routine cease to execute properly, then thecapacitor 324 will not be reset and theoscillator 318 will reset themicroprocessor 98. Correspondingly, the control signals the operator that an error is occurring by flashing adiagnostic LED 326. The output of theoscillator 318 is connected through aNAND gate 328 to the base of thenpn type transistor 330. Thetransistor 330 has an emitter connected to system ground through a current limitingresistor 332 and a collector connected to battery voltage +B through thedisagnostic LED 326. When theoscillator 318 reaches a "high" level, not only is themicroprocessor 98 reset, but thediagnostic LED 326 is also flashed at the frequency of theoscillator 318. If themicroprocessor 98 fails to respond to the reset signal, the flashing LED signals the operator as to the type of failure. - The control also has the ability to signal a number of different error messages to the operator via the
diagnostic LED 326. Another output from themicroprocessor 98 is connected to an input of theNAND gate 328 and to +5V via a pull upresistor 334. The software routine can energize thediagnostic LED 326 by placing a "low" signal on the output line. The type of error is communicated via a sequencing of theLED 326. For example, if a handle position is detected, which is outside the range of allowable movement, then the software flashes theLED 326 four times, pauses momentarily, and then repeats. Five flashes indicates that the hitch position signal is outside the acceptable range of movement. Similar codes can be established for a wide range of faults, thereby easing the job of troubleshooting a failed control. - Referring now to Figs. 4a, 4b and 4c a flowchart illustrates one embodiment of the software needed to operate the
microprocessor 98. The software begins atblock 234 by reaching the actual handle position and storing the instantaneous position in the variable Phandle. The microprocessor outputs the address of the handle position input and a start pulse of thedata link 102 and then monitors the end of conversion signal online 106. Upon receiving the signal via 106, the 8-bit word present onlink 100 is read and stored as Phandle. Control is transferred to block 235 where a desired hitch position is computed from the handle position and stored in the variable Pdes' Atblock 236 the actual hitch position is read via an operation substantially similar to that of reading the actual handle position with the exception of the address presented onlink 104 being that of the hitch position input. The actual hitch position is stored in variable Pact. -
- In
decision block 240, ameans 241 receives the positional error signal and delivers a desired velocity signal which has a magnitude correlative to the magnitude of the positional error signal. The variable Perr is multiplied by a constant k to convert the positional error into a desired velocity of thehitch 17. This simple equation ensures that as the positional error Perr becomes greater, so too does the desired velocity Vdes. Unchecked, this proportional relationship could lead to a desired hitch velocity Vdes which is above recommended operating speeds. To prevent this from occurring, the relationship k(P.rr) > Vmax is tested and if found to be true, then the desired velocity Vdes of thehitch 17 is set to a maximum allowable velocity Vmax in block 242. Conversely, if the tested relationship is false, then the desired velocity Vdes maintains its proportionality to the positional error and is set equal to k(Perr) in block 244. - Control is transferred to block 246 where the actual hitch velocity is read by the
microprocessor 98 via an operation similar to those performed inblocks block 248 using the equation: - A means receives the control signal and respectively controls the direction and velocity of movement of the
hitch 17 in a direction to reduce the absolute magnitude of the positional error signal and the control signal. Block 250 forms the integral of the velocity error Verr and transfers control to block 252. The sign of the positional error Perr is used to determine the direction of desired movement and correspondingly, which of thesolenoids block 254 by delivering a "low" signal from themicroprocessor 98 online 146 to enable NORgate 150 to pass the variable duty cycle signal from theamplifier 118 to thetransistor 158. Alternately, if the positional error Perr is less than zero, the up solenoid is selected inblock 256 by delivering a "high" signal from themicroprocessor 98 online 146 to enable NORgate 152 to pass the variable duty cycle signal from theamplifier 118 to thetransistor 170. - An opportunity to save energy and extend the life of the solenoids and the hydraulic system arises when the
hitch 17 has reached the upper travel limit. Typically, a certain degree of misalignment of the handle sensor is possible such that thehitch 17 cannot reach the desired position indicated by the handle 34. During normal operation, if the handle 34 is in the fully up position and thehitch 17 stops moving, then a software timer is initiated. If these conditions persist for a preselected duration of time, then block 258 transfers control to block 260 where the solenoid current is set to zero. Themicroprocessor 98 assumes that thehitch 17 has reached the maximum attainable height and shuts off power to the up solenoid. Subsequent movement of the handle 34 returns the software control to the normal mode of operation. - A similar mode of operation occurs when the handle 34 is not moved for an extended period of time and yet the
hitch 17 remains at a position higher than the desired position. Themicroprocessor 98 assumes that the hitch is unable to reach the commanded position due to either contact with the ground or a travel limiting stop. Should these conditions be satisfied, then control transfers to block 264 where the solenoid current is set to a minimal value to allow the hitch to float. Rather than fix the hitch position, it is desirable to allow the hitch to move up and down in contact with the ground surface. - Movement of the
hitch 17 is discontinued in response to the magnitude of the positional error signal Perr being within a first preselected range. Inblock 266, the software checks to determine if the hitch position is within an inner deadband. If the hitch has moved to within a preprogrammed distance of the desired position, then control transfers to theblock 260 where the solenoid current is set to zero and movement of thehitch 17 ceases. The threeway valve 302 returns to the center position and the pressure in thefeedback line 304 falls off significantly, causing the variable position swashplate to move to a low pressure standby position. The load on the engine is subsequently reduced resulting in a higher fuel efficiency. If the positional error is outside the inner deadband, the solenoid current is unaffected for the moment and control transfers to ablock 268 where the status of the hook up mode input is read. - For the operator to initiate the hook up mode, he must position the switch to the hook up mode and accomplish a preselected sequencing of the position handle 34. In the
block 270, the handle position is closely monitored to determine if the operator truly desires to be in the hook up mode and actuation of the switch was not accidental. To enter the hook up mode, the operator must position the handle 34 at the fully up, fully down, and middle position within a preselected duration of time. If the handle sequencing operation is not accomplished within the allotted time period, control transfers to theblock 260 and the solenoid current is set to zero. Assuming that the sequencing operation is completed, a flag is set so that the operator need not reproduce the sequence while the switch remains actuated. The software reads the handle position in block 272 and respectively selects the up or down solenoid inblocks 274, 276 if the handle 34 is in the fully up position or fully down position. Subsequently, inblock 278, the solenoid current is set to an intermediate constant value and causes a preselected rate of movement in the selected direction until the handle 34 is moved from the fully actuated position. A handle position other than fully up or fully down causes control to be transferred to theblock 260 where solenoid current is set to zero. Operation in the hook up mode allows the operator to accurately and absolutely position thehitch 17 by placing the handle 34 at the fully actuated position until the hitch a17 reaches the desired position. When thehitch 17 reaches the desired position, the operator simply moves the handle 34 from the fully actuated position and causes the solenoid current to be set to zero. - Control transfers to block 280 if the hook up mode switch is not actuated. Movement of the
hitch 17 is initiated in response to the magnitude of the position error Perr signal being outside a second preselected range. Withinblock 280, the status of a flag is checked to determine if the hitch position has been Inside the Inner deadband and Not Subsequently Outside an Outer deadband (IINSOO). If the flag is set, then control transfers to theblock 260 and solenoid current is set to zero; however, if the flag is not set, then control transfers to block 282 where the solenoid current is set to the integral of the velocity error plus an offset tmin. The IINSOO flag is necessary to allow the outer deadband to provide a hysteresis type effect during positioning of thehitch 17. Without the flag, the solenoid current would be set to zero when the positional error Perr fell below the outer deadband. Thehitch 17 would never reach the inner deadband. The outer deadband should only become operational subsequent to thehitch 17 reaching the inner deadband. Hence, the IINSOO flag is set when the positional error Perr falls inside the inner deadband and is reset when the positional error Per, rises above the outer deadband. - The solenoid offset current Imin is the current necessary to induce movement of the
hitch 17 at a minimum rate. Obviously, this current level is highly dependent upon a number of factors, including the individual solenoids and hydraulic components. It is therefore necessary to calibrate the offset current for each individual hitch control. A calibration mode can be entered in the software by executing a preselected sequence of handle 34 movements. Inblock 284, the position of the hook-up mode switch is monitored so that movement of the switch between the "on" and "off" positions a total of three iterations causes software control to be transferred into a current sourcing mode. Actual handle position is read via theAID 56 inblock 286.Decision block 288 compares the handle position to the upper limit of movement. When the handle is moved to the fully up position, the up solenoid is selected inblock 290 and the solenoid current is set to the offset Imin' Absent any movement of the handle 34 from the fully up position, the solenoid current will remain at the offset Imin and the solenoid controlled valve can be manually adjusted until thehitch 17 begins to move upward. Similarly, the handle position is compared to the lower limit inblock 294. The handle 34 being at the fully lowered postiion transfers control to block 296 where the down solenoid is selected. Once again, theblock 292 sets the solenoid current to the offset Imin, and the solenoid controlled down valve can be manually adjusted until thehitch 17 begins to move downward. Software control can be returned to the main control routine by a power- down and power-up with the vehicle key switch. - In the overall operation of the agricultural vehicle, assume that the operator is attempting to adjust the position of the
hitch 17 and an implement such as a plow under normal operating conditions. The operator adjusts the handle 34 to the desired height of depth of the plow and thecontroller 26 controllably modulates one of thevalves hitch 17 and plow is initiated toward the desired position at a rate dependent upon the magnitude of the positional error. The instantaneous velocity of thehitch 17 is constantly monitored and compared to the desired hitch velocity to arrive at a velocity error. Modulation of thevalves hitch 17 and plow in both the raise and lower conditions. - Should the handle 34 be moved to a position which is lower than the
hitch 17 can reach, for example, through contact with the ground surface, then the solenoid current is set to a value which allows the hitch to "float". Rather than overheat the solenoid by continuing to deliver maximum current, thecontroller 26 reduces current to a "float" value and allows thehitch 17 and plow to move up and down with undulations in the ground surface. Alternately, the handle 34 can also request a position which is higher than thehitch 17 can reach. In this instance, it is not necessary that thehitch 17 be allowed to "float", but it is sufficient to simply maintain thehitch 17 at the maximum height it can reach. Accordingly, the current to the solenoid is reduced to zero and thehitch 17 remains at the fully raised position. - When connecting an implement to the
hitch 17, the normal control mode can produce unexpected and undesirable movement of thehitch 17. For example, the handle 34 is requesting a position which thehitch 17 has reached, but due to a slight leakage of hydraulic fluid, thehitch 17 slowly descends until it reaches the outer deadband limit. At this point thecontroller 26 will energize the up solenoid and move thehitch 17 toward the desired position. This unexpected movement can cause misalignment of the hitch and plow and resultant difficulties in their connection. To eliminate these unpredictable movements during hook up, the operator enters an alternate mode of operation by actuating a switch and operating the handle through a preselected sequence of movements. In the hook up mode, the operator causes thehitch 17 to move up or down at a preselected rate by moving the handle 34 to the respective up and down limits of travel. The operator can now jog thehitch 17 into the desired position by selective movement of the handle 34 between an extreme position and a midrange position.
Claims (12)
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
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US06/881,412 US4852657A (en) | 1986-07-02 | 1986-07-02 | Apparatus for selectively positioning movable work element with preselected maximum velocity control |
US881412 | 1986-07-02 |
Publications (2)
Publication Number | Publication Date |
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EP0274501A1 EP0274501A1 (en) | 1988-07-20 |
EP0274501B1 true EP0274501B1 (en) | 1990-09-19 |
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Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
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EP87904468A Expired - Lifetime EP0274501B1 (en) | 1986-07-02 | 1987-07-01 | Three point hitch velocity control |
Country Status (8)
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US (1) | US4852657A (en) |
EP (1) | EP0274501B1 (en) |
JP (1) | JP2529322B2 (en) |
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BR (1) | BR8707375A (en) |
CA (1) | CA1319966C (en) |
SG (1) | SG6692G (en) |
WO (1) | WO1988000003A1 (en) |
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EP0523834B1 (en) * | 1991-06-03 | 1996-08-14 | New Holland U.K. Limited | Draft control system with closed loop drop/raise rate control of a hitch |
JPH0771412A (en) * | 1993-09-03 | 1995-03-17 | Kubota Corp | Hydraulic actuator operation structure for work vehicle |
US5697454A (en) * | 1995-07-18 | 1997-12-16 | Wilcox Brothers Incorporated | Three-point hitch assembly |
US5737993A (en) * | 1996-06-24 | 1998-04-14 | Caterpillar Inc. | Method and apparatus for controlling an implement of a work machine |
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US6250396B1 (en) | 1999-09-30 | 2001-06-26 | Caterpillar Inc. | Method and apparatus for controlling a hitch |
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- 1987-07-01 EP EP87904468A patent/EP0274501B1/en not_active Expired - Lifetime
- 1987-07-01 JP JP62504120A patent/JP2529322B2/en not_active Expired - Lifetime
- 1987-07-01 WO PCT/US1987/001525 patent/WO1988000003A1/en active IP Right Grant
- 1987-07-01 AU AU76461/87A patent/AU597401B2/en not_active Ceased
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GB2038507A (en) * | 1978-11-30 | 1980-07-23 | Zeiss Jena Veb Carl | Non-linear control system |
DE2927585B1 (en) * | 1979-07-07 | 1980-04-17 | Fendt & Co Xaver | Method and device for regulating the working depth of an agricultural tractor, e.g. a tractor-carried plow |
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Also Published As
Publication number | Publication date |
---|---|
CA1319966C (en) | 1993-07-06 |
US4852657A (en) | 1989-08-01 |
JPH01500163A (en) | 1989-01-26 |
SG6692G (en) | 1992-03-20 |
EP0274501A1 (en) | 1988-07-20 |
AU7646187A (en) | 1988-01-29 |
JP2529322B2 (en) | 1996-08-28 |
AU597401B2 (en) | 1990-05-31 |
WO1988000003A1 (en) | 1988-01-14 |
BR8707375A (en) | 1988-09-13 |
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